51 research outputs found
Electrochemically Controlled Proton-Transfer-Catalyzed Reactions at Liquid-Liquid Interfaces: Nucleophilic Substitution on Ferrocene Methanol
The generation of α-ferrocenyl carbocations from ferrocenyl alcohols for SN1 substitution at the waterâorganic solvent interface is initiated by the transfer of protons into the organic phase. The proton flux, and hence the reaction rate, can be controlled by addition of a suitable âphase-transfer catalystâ anion or by external polarization with a potentiostat, providing a new method for the synthesis of ferrocene derivatives
Parylene C Coated Microelectrodes For Scanning Electrochemical Microscopy
Herein, we present a simple microelectrode preparation methodology consisting in coating a platinum wire or a carbon fiber with a thin insulating Parylene C film (e.g. 1â10 ÎŒm), to produce SECM probes with a small and constant probe RG (i.e. ratio between the radius of the insulating sheath and the radius of the active electrode area). After exposition of a fresh active electrode area by blade cutting, a disc shaped electrode is obtained thanks to a protective hot mounting wax layer that avoids Parylene C coating deformation and is easily removed with acetone. Stiffness and straightness of the probe can be tuned by modifying the Parylene C coating thickness and the length of the carbon fiber or platinum wire. This simple electrode preparation method is highly reproducible (c.a. > 90%). The prepared Parylene C coated microelectrodes were characterized by optical microscopy, cyclic voltammetry, scanning electrochemical microscopy (SECM) approach curves and finally applied to SECM imaging of Pt band structures in contact-less and contact mode
Mechanism of oxygen reduction by metallocenes near liquid|liquid interfaces
The mechanism of the oxygen reduction reaction (ORR) at a liquid|liquid interface, employing ferrocene (Fc) derivatives â such as decamethylferrocene (DMFc) â as a lipophilic electron donor along with sulfuric acid as an aqueous proton source, was elucidated through comparison of experimentally obtained cyclic voltammograms (CVs) to simulated CVs generated through COMSOL Multiphysics software which employs the finite element method (FEM). The simulations incorporated a potential dependent proton transfer (i.e . ion transfer, IT) step from the water (w) to organic (o) phases along with two homogeneous reactions (C1C2) occurring in the organic phase â an IT-C1C2 mechanism. The reaction of DMFc with H+(o) to form DMFc-hydride (DMFc-H+) was considered the first step (reaction 1), while reaction of DMFc-H+ with oxygen to form a peroxyl radical species, View the MathML sourceHO2, and DMFc+ was deemed the second step (reaction 2). Subsequent reactions, between View the MathML sourceHO2 and either DMFc or H+, were considered to be fast and irreversible so that 2 was a âproton-sinkâ, such that further reactions were not included; in this way, the simulation was greatly simplified. The rate of 1, kcf, and 2, kchem, were determined to be 5 Ă 102 and 1 Ă 104 L molâ1 sâ1, respectively, for DMFc as the electron donor. Similarly, the rates of biphasic ORR for 1,1âČ-dimethylferrocene (DFc) and Fc were considered equivalent in terms of this reaction mechanism; therefore, their rates were determined to be 1 Ă 102 and 5 Ă 102 L molâ1 sâ1 for 1 and 2, respectively. The reactive and diffusive layer thicknesses are also discussed
Oxygen and hydrogen peroxide reduction by 1,2-diferrocenylethane at a liquid/liquid interface
Molecular oxygen and hydrogen peroxide reduction by 1,2-diferrocenylethane (DFcE) was investigated at a polarized water/1,2-dichloroethane (W/DCE) interface. The overall reaction points to a proton-coupled electron transfer (PCET) mechanism, where the first step consists of the protonation of DFcE to form the DFcEâH+ in DCE phase, either by DFcE facilitated proton transfer across the liquidâliquid interface or by the homogeneous protonation of DFcE in the presence of protons extracted in the oil phase by tetrakis(pentafluorophenyl)borate. The formation of DFcEâH+ is followed up by the O2 reduction to hydrogen peroxide and further reduction to water. The final products of DFcE oxidation, namely DFcE+ or DFcE2+, were investigated by ion transfer voltammetry, ultramicroelectrode voltammetry and UV/visible spectroscopy. These results show that mostly DFcE+ is produced, although DFcE+ can also reduce oxygen at longer time scales. Hydrogen peroxide reduction is actually faster than oxygen reduction, but both reactions are slow due to relatively low thermodynamic driving force
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